Factors for the Distribution of Polar Oases in Ellesmere Island, Arctic Canada, from the Viewpoint of Geoecology

抄録

In the Canadian High Arctic Region, there stretches a desert-like barren landscape. However, dense lush meadows called polar oases are found around Alexandra Fiord and Sverdrup Pass in the central part of Ellesemere Island. Freedman et al. (1994) asserted that polar oases are formed because the steep cliffs surrounding the lowland reflect the sunlight and radiate infrared rays which warm the area. They called this the “oven-effect.” However, under the midnight sun a favorable result has not come out. The author studied the factors affecting the distribution of polar oases from the viewpoint of geoecology, and found that geology is the most important factor which controls the distribution of polar oases. Around Sverdrup Pass the meadows are distributed in the lowland and on the north-faced slopes of the southern mountains, while on the northern mountains vegetation is scanty. Such a difference of plant cover developing between the northern and southern mountains cannot be explained by the oven-effect, but by difference of geology. The author considers that the difference of stability of slope deposits has brought about the extreme difference in plant coverage. The meadows appear mainly on the glacial deposits in the granite area. The reason is that the glacial till is composed of boulder, gravel and sand, thus stable enough for the development of plant communities. On the other hand, in the dolomite areas of the northern mountains active frost-shattering produces debris and also freeze-thaw action causes active debris movement. Therefore, the slope deposits are unstable and thus vegetation is scanty. In the polar region with the midnight sun, it seems that there is the possibility for meadows to be formed at any location. However, the granite areas that are suitable for plant growth are extremely limited, and thus the distribution of polar oases is also limited. In the dolomite areas that occupy most of the High Arctic, the regosol is unstable and the development of plant communities is hindered, and thus the meadows are hardly formed. The author considers this is the reason why the originally natural lush meadows are conspicuous in the lowland and on the northfaced slopes of the southern mountains around Sverdrup Pass.